A steam turbine plant includes a steam turbine and a piping system including piping in which steam flows. The piping of the piping system includes steam piping in which the steam to be supplied to the steam turbine flows and bypass piping branching from the steam piping. The steam generated in a steam generation device including a heating unit is supplied to the steam turbine through the steam piping of the piping system. At the time of start of the steam turbine plant or at the time of an excessive increase in pressure in the steam piping, the steam flows in the bypass piping. The steam is supplied to the bypass piping at the time of start of the steam turbine plant, thereby to improve starting performance of the steam turbine plant.
Blowing out (flushing) to remove foreign substances in the piping is conducted before the start of the steam turbine plant after completion of construction for building the steam turbine plant, after completion of alteration, or after long-term suspension. The blowing out includes processing of supplying steam to the piping. The foreign substances in the piping are blown out by the steam supplied to the piping. Accordingly, the foreign substances in the piping are removed. The steam supplied to the piping in the blowing out is free-blown (released into the atmosphere). An example of the technology regarding the blowing out is disclosed in Patent Literature 1.